Numerous control means have already been proposed for automatically returning the switches designed for controlling change-of-direction indicators to the rest position.
In most cases, these control means comprise a control lever pivotally mounted on a support together with a controlling cam fixed to the steering wheel shaft, i.e. to the shaft connected to the steering wheel and used for swivelling the steerable wheels.
A first prior embodiment of such control means is shown in French patent specification FR-A-2 515 865 or in French patent application number FR-86 16924 filed 3rd December 1986 by the present Assignee. In this first embodiment, the control means comprise a contact-carrying equipment associated with an indexing system, a return finger, two symmetrical traction springs, a forcing slide, and a forcing spring. The contact-carrying equipment is provided with a cut-out delimited by a W-shaped border. The forcing slide is provided with an oblong slot which is radial relative to the axis of the steering wheel shaft. The return finger carries two opposite stub axles engaged respectively in the cut-out and in the slot. The traction springs urge the return finger towards the control cam. However, in the rest position, when none of the change-of-direction indicators is switched on, one of the stub axles rests against the middle point of the W-shaped cut-out, and the finger is at a distance from the control cam. In a working position, while the contact-carrying equipment is pivoted and one of the change-of-direction indicators is switched on, the stub axles are displaced radially in the cut-out and in the slot, moving closer towards the shaft. The finger enters into the displacement sector of the control cam. For one direction of shaft rotation, the control cam causes the finger to pivot about the axis of the stub axles without acting on the contact-carrying equipment. For the opposite direction of rotation, the control cam drives the finger to return the contact-carrying equipment to the rest position. The forcing spring and slide prevent the device from being damaged if the driver holds the switch in the working position while the steering wheel shaft is rotating in such a direction as to tend to return the switch to the rest position. These control means have already provided good service. However, they comprise a relatively large number of parts.
A second known way of implementing such control means is shown in U.S. Pat. No. 4 393 280. In this second embodiment, the control means comprise a contact-carrying equipment which surrounds the steering wheel shaft, a cam carried by the equipment opposite to the control lever about the steering wheel shaft and serving to co-operate with the control cam, and a spring interposed between the cam and the contact-carrying equipment. These control means have also provided good service. However, since the contact-carrying equipment surrounds the steering wheel shaft, the switch must be installed axially with the steering wheel removed.
A third prior implementation of such control means is shown in French patent specification FR-A-2 076 682. In this third embodiment, the control means comprise at least one wheel suitable for rolling with friction against the steering wheel shaft, a gear wheel fixed to the rolling wheel, a toothed sector suitable for engaging the gear wheel when the associated control lever is pivoted, and a spring engaged with the toothed sector. These control means have also provided good service. However, they comprise a relatively large number of parts. Further, in operation, they depend to a large extent on the magnitude of the friction force exerted by the rolling wheel on the steering wheel shaft. In practice, it is observed that this force tends to reduce considerably in use.
A fourth prior implementation of the control means is shown in U.S. Pat. No. 4 315 117. In this fourth embodiment, the control means comprise a circular equipment rotably mounted on a support plate and provided with two peripheral concave index notches, a locking yoke resting against the equipment, a lever pivotally mounted on the yoke, and a traction spring interposed between the yoke and the lever. When the equipment is moved to the working position to switch on one of the change-of-direction indicators, the locking yoke penetrates into one of the concave index notches. The equipment is returned to the rest position when the steering wheel shaft is rotated in an appropriate direction and the control cam displaces the lever in a direction tending to urge the yoke out from the above-mentioned concave notch. These control means have also provided good service. However, they are constituted by a relatively large number of parts.
A fifth prior implementation of such control means is shown in German patent specification No. 3 430 664. In this fifth embodiment, the control means comprise an equipment associated with the control lever and pivotally mounted on a support plate, a cam which is pivotally mounted on the equipment and which co-operates with the control cam, and a spring interposed between the cam and the equipment in order to urge the cam towards a rest position relative to the control cam. These control means have already provided good service. However, they require structures of relatively complex parts, in particular with respect to the pivoting equipment which in turn supports the pivoting cam.